Another challenge is that of reliable state preparation.
In particular, a key experimental goal highlighted by this work is to gain access to  high-quality GKP qubits whose teeth are squeezed at or exceeding the 15 dB level. This motivates the improvement of existing methods for state generation with GBS devices, which previously considered states with up to 10 dB of per-peak squeezing [1]}, [2]}, [3]}, [4]}. Reaching 15 dB states with the techniques from Refs. [1]}, [2]}, [3]}, [4]} will involve going to higher-order truncations of the Fock basis, which is computationally more demanding. This motivates the development of new numerical simulation techniques, or the application of breeding or distillation protocols to lower quality states to reach the 15 dB level. Progress in these directions is critical to accurate resource estimates for photonic quantum computing.
Though the present architecture only couples GBS devices to optical switches, we leave open the possibility of using any surplus GKP qubits to check and improve the quality of outputs, for example, by using them as flag qubits [9]}.
Overhead, particularly the required number of bosonic qubit states, can be reduced by using fore-knowledge about the quantum computation. For example, we expect there to be little (if any) benefit to having bosonic qubits in place of squeezed states at \(q\) -measured nodes described in sec:FTQC.
